Discharge control apparatus and method

ABSTRACT

A discharge control apparatus for controlling a flyback power supply circuit which includes a transformer having a primary coil and a secondary coil and performing voltage conversion, and a driver for controlling energization of the primary coil. The power supply circuit supplies electric energy to a plasma reactor. The discharge control apparatus calculates, based on primary current flowing through the primary coil and primary voltage generated in the primary coil, supply energy supplied to the primary coil and regeneration energy which is a portion of the supply energy not used for the discharge in the plasma reactor. The discharge control apparatus controls the power supply circuit based on the calculated supply energy and the calculated regeneration energy. Also disclosed is a method for controlling the flyback power supply circuit.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a discharge control apparatus forcontrolling a power supply circuit which supplies electric energy to aplasma reactor, and to a discharge control method for controlling thepower supply circuit.

2. Description of the Related Art

Patent Document 1 describes an application voltage control apparatuswhich detects current flowing to a plasma reactor as a result ofgeneration of a pulse-like secondary voltage of a step-up circuit, andestimates the value of application voltage applied to the plasma reactorbased on an integral current value obtained by integrating the detectedcurrent value.

[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No2017-16858

3. Problems to be Solved by the Invention

In the technique described in Patent Document 1, the current on thesecondary side is directly detected and used to control the plasmareactor. Since the secondary voltage of the step-up circuit is a highvoltage of several kilovolts, the current detection must be performed ina state in which insulation is secured by using, for example, anon-contact-type current sensor. Therefore, the technique described inPatent Document 1 requires a component or assembly for insulating thecurrent sensor which may result in increased production cost andcomplexity of the apparatus.

SUMMARY OF THE INVENTION

It is therefore an object of the present disclosure to reduce productioncost or simplify the structure of a control apparatus for controlling aflyback power supply circuit.

The above object has been achieved by providing (1) a discharge controlapparatus for controlling a flyback power supply circuit. The powersupply circuit comprises a transformer having a primary coil and asecondary coil and which performs voltage conversion, and a driver forcontrolling energization of the primary coil. The power supply circuitsupplies electric energy to a plasma reactor which generates plasma bydischarge.

The discharge control apparatus of the present disclosure comprises anenergy calculation section and a control section.

The energy calculation section is configured to calculate, based onprimary current flowing through the primary coil and primary voltagegenerated in the primary coil, supply energy supplied to the primarycoil and regeneration energy which is a portion of the supply energy notused for the discharge in the plasma reactor.

The control section is configured to control the power supply circuitbased on the supply energy and regeneration energy calculated by theenergy calculation section.

The discharge control apparatus of the present disclosure configured asdescribed above calculates the supply energy and the regeneration energybased on the primary current flowing through the primary coil and theprimary voltage generated in the primary coil, and controls the powersupply circuit based on the supply energy and regeneration energy. Byvirtue of this configuration, the discharge control apparatus of thepresent disclosure can control the power supply circuit without use ofsecondary current flowing through the secondary coil and secondaryvoltage generated in the secondary coil. Therefore, the dischargecontrol apparatus of the present disclosure can eliminate the necessityof a component or assembly for securing insulation, thereby reducingproduction cost or simplifying apparatus configuration.

In a preferred embodiment (2) of the discharge apparatus (1) of thepresent disclosure, the energy calculation section calculates the supplyenergy in accordance with the following Equation (1) and calculates theregeneration energy in accordance with the following Equation (2). Thesupply energy is denoted by E_(sup). The regeneration energy is denotedby E_(reg). The value of the primary current is denoted by I_(p). Thevalue of the primary voltage is denoted by V_(p). The time period duringwhich the supply energy is generated is denoted a period from time t₁ totime t₂, and the time period during which the regeneration energy isgenerated is denoted a period from time t₃ to time t₅.

[Expression 1]

E _(sup)=∫_(t) ₁ ^(t) ² V _(p) ·I _(p) dt  (1)

E _(reg)=∫_(t) ₃ ^(t) ⁵ V _(p) ·I _(p) dt  (2)

In a second aspect, the present disclosure provides (3) a dischargecontrol method for controlling a flyback power supply circuit.

The discharge control method comprises an energy calculation step and acontrol step.

The energy calculation comprises calculating the supply energy suppliedto the primary coil and the regeneration energy which is a portion ofthe supply energy not used for the discharge in the plasma reactor basedon the primary current flowing through the primary coil and the primaryvoltage generated in the primary coil.

The control step comprises controlling the power supply circuit based onthe supply energy and the regeneration energy calculated by the energycalculation step.

Since the discharge control method of the present disclosure is executedby the discharge control apparatus of the present disclosure, effectssimilar to those obtained by the discharge control apparatus of thepresent disclosure can be obtained by performing the method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the schematic configuration of apurification system.

FIG. 2 is a circuit diagram showing the configurations of a plasmareactor, a transformer, and a discharge control apparatus.

FIG. 3 is a flowchart showing a discharge control process.

FIG. 4 is a flowchart showing an initial diagnosing process.

FIG. 5 is a flowchart showing a purification-time diagnosing process.

FIG. 6 is a circuit diagram showing flows of energy due to discharge.

FIG. 7 is a timing chart showing changes in PWM signal, primary current,primary inter-terminal voltage, and secondary energy.

FIG. 8 is a timing chart showing changes in PWM signal, primary current,primary inter-terminal voltage, and flyback voltage.

FIG. 9 is a diagram showing an equivalent circuit of the plasma reactor.

FIG. 10 is a timing chart showing a specific example of operation of thedischarge control apparatus.

DESCRIPTION OF REFERENCE NUMERALS

Reference numerals used to identify various features in the drawingsinclude the following.

3 . . . plasma reactor, 4 . . . transformer, 6 . . . discharge controlapparatus, 21 . . . primary coil, 22 . . . secondary coil, 32 . . .driver

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present disclosure will next be described ingreater detail with reference to the drawings. However, the presentdisclosure should not be construed as being limited thereto.

As shown in FIG. 1, a purification system 1 of the present embodimentincludes an electronic control apparatus 2, a plasma reactor 3, atransformer 4, a battery 5, a discharge control apparatus 6, andtemperature sensors 7 and 8.

The electronic control apparatus 2 controls an engine of a vehicle onwhich the purification system 1 is mounted. In the followingdescription, the electronic control apparatus 2 will be referred to asthe engine ECU 2. ECU is an abbreviation for Electronic Control Unit.

The plasma reactor 3 generates plasma by dielectric barrier discharge.As a result, the plasma reactor 3 removes particulate matter,hydrocarbons, etc., contained in exhaust gas discharged from the engineof the vehicle.

The transformer 4 outputs a high voltage for driving the plasma reactor3. The battery 5 supplies a power supply voltage VB to the engine ECU 2,the transformer 4, and the discharge control apparatus 6.

The discharge control apparatus 6 controls the discharge by the plasmareactor 3 through switching between an energization state in whichcurrent flows to the transformer 4 and a non-energization state in whichno current flows to the transformer 4. The discharge control apparatus 6performs data communication with the engine ECU 2 through acommunication line.

The temperature sensor 7 detects the temperature of the transformer 4and outputs to the discharge control apparatus 6 a detection signalrepresenting the detected temperature of the transformer 4. Thetemperature sensor 8 detects the temperature of a driver 32 which isprovided in the discharge control apparatus 6 described below. Thetemperature sensor 8 outputs to the discharge control apparatus 6 adetection signal representing the detected temperature of the driver 32.Notably, the driver 32 is shown in FIG. 2.

As shown in FIG. 2, the plasma reactor 3 includes a plurality of firstelectrode panels each of which includes a discharge electrode 11embedded therein, and a plurality of second electrode panels each ofwhich includes a discharge electrode 12 embedded therein. The firstelectrode panels and the second electrode panels are disposedalternatingly along the flow direction of the exhaust gas atpredetermined intervals. The plasma reactor 3 generates plasma as aresult of application of voltage between the first and second electrodepanels located adjacent to each other.

The transformer 4 includes a primary coil 21 and a secondary coil 22.One end of the primary coil 21 is connected to the positive terminal ofthe battery 5, and the other end of the primary coil 21 is connected tothe discharge control apparatus 6. One end of the secondary coil 22 isconnected to the discharge electrode 11 of the plasma reactor 3, and theother end of the secondary coil 22 is connected to the dischargeelectrode 12 of the plasma reactor 3.

When the discharge control apparatus 6 brings the transformer 4 into theabove-described energization state, current flows to the primary coil 21and energy is stored therein. Subsequently, when the discharge controlapparatus 6 brings the transformer 4 into the above-describednon-energization state, the supply of current to the primary coil 21 iscut off. As a result, the energy stored in the primary coil 21 isconveyed to the secondary coil 22, and high voltage is generated in thesecondary coil 22. Namely, the transformer 4 generates high voltage in aflyback configuration.

The discharge control apparatus 6 includes a microcomputer 31, a driver32, a gate driver 33, a resistor 34, current integration circuits 35 and36, a current detection circuit 37, a regeneration detection circuit 38,and voltage detection circuits 39 and 40.

The microcomputer 31 includes a CPU 51, a ROM 52, and a RAM 53. Thevarious functions of the microcomputer are realized by a program whichis stored in a non-transitory tangible recording medium and executed bythe CPU 51. In this example, the ROM 52 corresponds to thenon-transitory tangible recording medium storing the program. Also, amethod corresponding to the program is performed as a result ofexecution of this program. Notably, some or all of the functions of theCPU 51 may be realized by hardware; for example, by a single IC or aplurality of ICs. The discharge control apparatus 6 may include a singlemicrocomputer or a plurality of microcomputers.

The microcomputer 31 has a voltage output terminal 54 and voltage inputterminals 55, 56, 57, 58, and 59.

The driver 32 is an N-channel-type MOSFET. The drain of the driver 32 isconnected to the primary coil 21 of the transformer 4. The source of thedriver 32 is grounded through the resistor 34.

The input terminal of the gate driver 33 is connected to the voltageoutput terminal 54 of the microcomputer 31 through a resistor 41. Theoutput terminal of the gate driver 33 is connected to the gate of thedriver 32 through a resistor 42. The gate driver 33 receives a PWMsignal output from the voltage output terminal 54 of the microcomputer31 and outputs, in accordance with the voltage level of the PWM signal,a gate control voltage V_(gs) applied to the gate of the driver 32 forswitching the driver 32 between on and off states. Specifically, whenthe PWM signal is at a high level, the gate driver 33 switches the gatecontrol voltage V_(gs) to a high level, and when the PWM signal is at alow level, the gate driver 33 switches the gate control voltage V_(gs)to a low level. PWM is an abbreviation for Pulse Width Modulation.

The driver 32 assumes an on state when the gate control voltage V_(gs)applied to the gate is at a high level. As a result, current flowsbetween the drain and the source of the driver 32. Meanwhile, the driver32 assumes an off state when the gate control voltage V_(gs) applied tothe gate is at a low level. As a result, the flow of current between thedrain and the source of the driver 32 stops.

One end of the resistor 34 is connected to the source of the driver 32,and the other end of the resistor 34 is grounded.

The current integration circuit 35 includes an operational amplifier 61,a resistor 62, and a capacitor 63. The non-inverting input terminal ofthe operational amplifier 61 is connected to the one end of the resistor34. The inverting input terminal of the operational amplifier 61 isconnected to the other end of the resistor 34 through the resistor 62.The output terminal of the operational amplifier 61 is connected to thevoltage input terminal 58. One end of the capacitor 63 is connected tothe output terminal of the operational amplifier 61, and the other endof the capacitor 63 is connected to the inverting input terminal of theoperational amplifier 61. The current integration circuit 35 configuredas described above outputs a supply current integration voltage V_(isi)by integrating, with time, the voltage generated across the resistor 34when a current flows through the resistor 34 from the driver 32 sidetoward the ground side.

The current integration circuit 36 includes an operational amplifier 66,a resistor 67, and a capacitor 68. The non-inverting input terminal ofthe operational amplifier 66 is connected to the other end of theresistor 34. The inverting input terminal of the operational amplifier66 is connected to the one end of the resistor 34 through the resistor67. The output terminal of the operational amplifier 66 is connected tothe voltage input terminal 59. One end of the capacitor 68 is connectedto the output terminal of the operational amplifier 66, and the otherend of the capacitor 68 is connected to the inverting input terminal ofthe operational amplifier 66. The current integration circuit 36configured as described above outputs a regeneration current integrationvoltage V_(iri) by integrating, with time, the voltage generated acrossthe resistor 34 when a current flows through the resistor 34 from theground side toward the driver 32 side.

The current detection circuit 37 includes an operational amplifier 71and resistors 72, 73, 74, and 75. The output terminal of the operationalamplifier 71 is connected to the voltage input terminal 57. The resistor72 is connected between the one end of the resistor 34 and thenon-inverting input terminal of the operational amplifier 71. A voltageV1 (in the present embodiment, for example, 2.5 V) is applied to one endof the resistor 73, and the other end of the resistor 73 is connected tothe non-inverting input terminal of the operational amplifier 71. Theresistor 74 is connected between the other end of the resistor 34 andthe inverting input terminal of the operational amplifier 71. Theresistor 75 is connected, as a feedback resistor, between the invertinginput terminal and the output terminal of the operational amplifier 71.Namely, a differential amplification circuit is formed by theoperational amplifier 71 and the resistors 72, 73, 74, and 75.Therefore, the operational amplifier 71 outputs a voltage V_(ip) byamplifying the voltage generated across the resistor 34. Theregeneration detection circuit 38 includes an operational amplifier 81,resistors 82 and 83, and a capacitor 84. The inverting input terminal ofthe operational amplifier 81 is connected to the other end of theresistor 34 through the resistor 75 and the resistor 74. The outputterminal of the operational amplifier 81 is connected to the invertinginput terminal of the operational amplifier 61 through a resistor 43 anda diode 44. Further, the output terminal of the operational amplifier 81is connected to the input terminal of the gate driver 33 through aresistor 23. Therefore, the gate driver 33 switches the gate controlvoltage V_(gs) to a high level when the output signal from theregeneration detection circuit 38 is at a high level, and switches thegate control voltage V_(gs) to a low level when the output signal fromthe regeneration detection circuit 38 is at a low level.

One end of the resistor 82 is connected to the non-inverting inputterminal of the operational amplifier 81, and the other end of theresistor 82 is grounded. A voltage V2 (in the present embodiment, forexample, 5 V) is applied to one end of the resistor 83, and the otherend of the resistor 83 is connected to the non-inverting input terminalof the operational amplifier 81. One end of the capacitor 84 isconnected to the output terminal of the operational amplifier 81, andthe other end of the capacitor 84 is connected to the inverting inputterminal of the operational amplifier 81.

The voltage detection circuit 39 includes resistors 91 and 92. One endof the resistor 91 is connected to the positive terminal of the battery5, and the other end of the resistor 91 is connected to the voltageinput terminal 55. One end of the resistor 92 is connected to thevoltage input terminal 55, and the other end of the resistor 92 isgrounded.

The voltage detection circuit 40 includes resistors 96 and 97. One endof the resistor 96 is connected to the other end of the primary coil 21,and the other end of the resistor 96 is connected to the voltage inputterminal 56. One end of the resistor 97 is connected to the voltageinput terminal 56, and the other end of the resistor 97 is grounded.

The voltage output terminal 54 is connected to the inverting inputterminal of the operational amplifier 66 through a resistor 45 and adiode 46.

Next, the steps of a discharge control process executed by the CPU 51 ofthe discharge control apparatus 6 will be described. The dischargecontrol process is started immediately after the microcomputer 31 startsits operation upon supply of power to the discharge control apparatus 6as a result of switching of an accessory power supply of the vehiclefrom an off state to an on state.

As shown in FIG. 3, in the discharge control process, the CPU 51 firstexecutes an initial diagnosing process in S20.

Here, the steps of the initial diagnosing process will be described.

As shown in FIG. 4, in initial diagnosing process, the CPU 51 firstdiagnoses an anomaly of the internal temperature of the transformer 4 inS110. Specifically, the CPU 51 determines whether or not the temperatureindicated by the detection signal from the temperature sensor 7(hereinafter referred to as the “power supply circuit internaltemperature”) falls within a predetermined operating temperature range(in the present embodiment, for example, −40° C. to +85° C.) setbeforehand. In the case where the power supply circuit internaltemperature falls within the operating temperature range, the CPU 51clears an initial temperature anomaly flag provided in the RAM 53.Meanwhile, in the case where the power supply circuit internaltemperature falls outside the operating temperature range, the CPU 51sets the initial temperature anomaly flag.

Next, in S120, the CPU 51 diagnoses an anomaly of the voltage of thebattery 5. Specifically, the CPU 51 determines, based on the voltageinput from the voltage detection circuit 39 to the voltage inputterminal 55, whether or not the voltage of the battery 5 (hereinafterreferred to as the “power supply voltage”) falls within an operatingvoltage range (in the present embodiment, for example, 10 V to 16 V) setbeforehand. In the case where the power supply voltage falls within theoperating voltage range, the CPU 51 clears an initial voltage anomalyflag provided in the RAM 53. Meanwhile, in the case where the powersupply voltage falls outside the operating voltage range, the CPU 51sets the initial voltage anomaly flag.

Next, in S130, the CPU 51 diagnoses an internal failure of thetransformer 4. Specifically, the CPU 51 first outputs from the voltageoutput terminal 54 a PWM signal having a previously set duty ratio forinitial diagnosis. As a result, the plasma reactor 3 generates dischargeat an energy level lower than that for the discharge generated in S50described below, thereby generating plasma. When the driver 32 is in theon state, the CPU 51 determines, based on the voltage V_(ip) input fromthe current detection circuit 37 to the voltage input terminal 57,whether or not the magnitude of the current having flowed to the primarycoil 21 (hereinafter referred to as the “primary coil current value”) issmaller than a transformer wire-breakage determination value setbeforehand. In the case where the primary coil current value is smallerthan the transformer wire-breakage determination value, the CPU 51 setsan initial wire-breakage anomaly flag provided in the RAM 53. Meanwhile,in the case where the primary coil current value is equal to or largerthan the transformer wire-breakage determination value, the CPU 51clears the initial wire-breakage anomaly flag.

Next, in S140, the CPU 51 diagnoses a leakage anomaly of the plasmareactor 3.

First, a method of detecting a short circuit of the plasma reactor 3will be described.

As shown in FIG. 6, when the driver 32 is switched from the off state tothe on state, a primary current I_(p) flows to the primary coil 21, andan inter-terminal voltage V_(p) of the primary coil 21 (hereinafterreferred to as the “primary inter-terminal voltage V_(p)”) is generated,whereby supply energy E_(sup) is stored in the primary coil 21. When thedriver 32 is switched from the on state to the off state after that, thesupply energy E_(sup) stored in the primary coil 21 is conveyed to thesecondary coil 22. As a result, a high voltage is generated in thesecondary coil 22, and discharge is generated in the plasma reactor 3.At that time, a flyback voltage V_(fly) is generated between the drainand the source of the driver 32.

The inter-terminal voltage of the secondary coil 22 will be referred toas the “secondary inter-terminal voltage V_(s).” The energy consumed bythe discharge in the plasma reactor 3 will be referred to as the“discharge energy E_(dis).” Since the plasma reactor 3 is a capacitiveload, the energy not consumed by the discharge is returned to theprimary side. This energy will be referred to as the “regenerationenergy E_(reg).”

Accordingly, a relation represented by Equation (3) holds between thesupply energy E_(sup) and “the discharge energy E_(dis) and theregeneration energy E_(reg).” When the discharge energy E_(dis) issmall, the supply energy E_(sup) and the regeneration energy E_(reg) areapproximately equal to each other. Namely, a relation represented byEquation (4) holds between the supply energy E_(sup) and theregeneration energy E_(reg). In the case where a leakage current flowsin the plasma reactor 3, a relation represented by Equation (5) holds,where E_(leak) represents the leakage energy which is the energyconsumed as a result of the flow of the leak current in the plasmareactor 3.

Therefore, when a leakage current flows within the plasma reactor 3 in astate in which the discharge energy E_(dis) is small, a relationrepresented by Equation (6) holds.

[Expression 2]

E _(sup) =E _(reg) +E _(dis)  (3)

E _(sup) ≅E _(reg)  (4)

E _(sup) =E _(reg) +E _(leak)  (5)

E _(sup) >E _(reg)  (6)

As shown in FIG. 7, when the PWM signal changes from the low level tothe high level at time t₁, the primary current I_(p) increasesgradually, and the primary inter-terminal voltage V_(p) becomes equal tothe power supply voltage VB. Subsequently, when the PWM signal changesfrom the high level to the low level at time t₂, the primary currentI_(p) decreases sharply and becomes 0 [A], the primary inter-terminalvoltage V_(p) decreases sharply to the negative side from the powersupply voltage VB, and discharge is generated in the plasma reactor 3.The generation of discharge continues from time t₂ to time t₃. After thedischarge ends, the primary current I_(p) attenuates while oscillatingon the negative side, and becomes 0 [A] at time t₄. The primaryinter-terminal voltage V_(p) becomes equal to the power supply voltageVB in the period between time t₃ and time t₄, and becomes 0 [V] at timet₄. Subsequently, the state in which the primary current I_(p) is 0 I[A]and the primary inter-terminal voltage V_(p) is 0 [V] continues up totime t₅ when the PWM signal again changes from a low level to a highlevel.

Namely, the period from time t₁ to time t₂ is an energy supply periodT_(sup). The period from time t₂ to time t₃ is a discharge periodT_(dis). The period from time t₃ to time t₄ is a regeneration periodT_(reg).

In FIG. 8, a curve L1 represented by a broken line shows the primarycurrent I_(p) for the case where a leakage current flows in the plasmareactor 3. A curve L2 represented by a broken line and a bent line L3represented by a broken line show the primary inter-terminal voltageV_(p) for the case where a leakage current flows in the plasma reactor3. A curve L4 represented by a continuous line shows the primary currentI_(p) for the case where no leakage current flows in the plasma reactor3. As shown by the curves L1 and L4, when a leakage current flows in theplasma reactor 3, the absolute value of the primary current I_(p) in theregeneration period T_(reg) decreases. Therefore, when a leakage currentflows in the plasma reactor 3, the regeneration energy E_(reg)decreases.

Accordingly, in S140, the CPU 51 first outputs from the voltage outputterminal 54 a PWM signal having a previously set duty ratio for initialdiagnosis. The duty ratio for initial diagnosis is set so as toestablish a no-discharge state in which no discharge is generated in theplasma reactor 3 or a low discharge state in which the discharge energyin the plasma reactor 3 is small. Notably, the expression “the dischargeenergy is small” means that the amount of discharge is, for example, 10%or less of the maximum discharge amount of the plasma reactor 3.

The CPU 51 then calculates the supply energy E_(sup) in accordance withEquation (7) based on the supply current integration voltage V_(isi)input to the voltage input terminal 58. The CPU 51 also calculates theregeneration energy E_(reg) in accordance with Equation (8) on the basisof the regeneration current integration voltage V_(iri) input to thevoltage input terminal 59.

Notably, R_(sh) in Equations (7) and (8) represents the resistance ofthe resistor 34. R_(gs) in Equation (7) represents the resistance of theresistor 62. C_(gs) in Equation (7) represents the capacitance of thecapacitor 63. R_(gr) in Equation (8) represents the resistance of theresistor 67. C_(gr) in Equation (8) represents the capacitance of thecapacitor 68.

The supply energy E_(sup) calculated in accordance with Equation (7)corresponds to the supply energy E_(sup) calculated in accordance withEquation (9). The regeneration energy E_(reg) calculated in accordancewith Equation (8) corresponds to the regeneration energy E_(reg)calculated in accordance with Equation (10). Time t₁ in Equation (9)corresponds to time t₁ in FIG. 7. Time t₂ in Equation (9) corresponds totime t₂ in FIG. 7. Time t₃ in Equation (10) corresponds to time t₃ inFIG. 7. Time t₅ in Equation (10) corresponds to time t₅ in FIG. 7.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\{E_{\sup} = {\frac{C_{gs}R_{gs}V_{isi}}{R_{sh}} \times {VB}}} & (7) \\{E_{reg} = \frac{C_{gr}R_{gr}V_{iri}}{R_{sh}}} & (8) \\{E_{\sup} = {\int_{t_{1}}^{t_{2}}{{V_{p} \cdot I_{p}}{dt}}}} & (9) \\{E_{reg} = {\int_{t_{3}}^{t_{5}}{{V_{p} \cdot I_{p}}{dt}}}} & (10)\end{matrix}$

Subsequently, the CPU 51 determines whether or not the calculated supplyenergy E_(sup) and the calculated regeneration energy E_(reg) satisfythe relation represented by Equation (6). Namely, the CPU 51 determineswhether or not the supply energy E_(sup) is larger than the regenerationenergy E_(reg). In the case where the supply energy E_(sup) is largerthan the regeneration energy E_(reg), the CPU 51 sets an initial leakageflag provided in the RAM 53. Meanwhile, in the case where the supplyenergy E_(sup) is equal to or smaller than the regeneration energyE_(reg), the CPU 51 clears the initial leakage flag.

After completing the process of S140, as shown in FIG. 4, the CPU 51diagnoses an open anomaly of the plasma reactor 3 in S150. The openanomaly of the plasma reactor 3 means the occurrence of breakage of theplasma reactor 3 or wire breakage in the plasma reactor 3.

First, a method of detecting the open anomaly of the plasma reactor 3will be described.

As shown in FIG. 9, the equivalent circuit of the plasma reactor 3 isrepresented by a capacitor 16 and a capacitor 17 connected in series tothe capacitor 16.

When the capacitance of the plasma reactor 3 is denoted by C_(c), thecapacitance of the capacitor 16 is denoted by C_(g), and the capacitanceof the capacitor 17 is denoted by C_(d), the capacitance of the plasmareactor 3 is represented by Equation (1). Notably, C_(d)>C_(g).

The supply energy E_(sup) is represented by Equation (12). The secondaryinter-terminal voltage V_(s) is represented by Equation (13) obtainedfrom Equation (12).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack & \; \\{C_{c} = \frac{C_{d}C_{g}}{C_{d} + C_{g}}} & (11) \\{E_{\sup} = {\frac{1}{2} \cdot C_{c} \cdot V_{s}^{2}}} & (12) \\{V_{s} = \sqrt{\frac{2\; E_{\sup}}{C_{c}}}} & (13)\end{matrix}$

When the number of turns of the primary coil 21 is denoted by n and thenumber of turns of the secondary coil 22 is denoted by m, the flybackvoltage V_(fly) is represented by Equation (14). Therefore, the flybackvoltage V_(fly) is represented by Equation (15) obtained from Equation(13) and Equation (14).

When breakage or wire breakage occurs in the plasma reactor 3, thecapacitance C_(d) of the capacitor 17 decreases. When the capacitance ofthe capacitor 17 in a state in which the plasma reactor 3 is broken orsuffers wire breakage is denoted by C_(do), the relation represented byEquation (16) holds.

Further, when the capacitance of the plasma reactor 3 in a state inwhich the plasma reactor 3 is broken or suffers wire breakage is denotedby C_(open), the relation represented by Equation (17) holds.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack & \; \\{V_{fly} = {\frac{n}{m} \cdot V_{s}}} & (14) \\{V_{fly} = {\frac{n}{m} \cdot \sqrt{\frac{2\; E_{\sup}}{C_{c}}}}} & (15) \\{C_{do}C_{g}} & (16) \\{C_{open} = {\frac{C_{do}C_{g}}{C_{do} + C_{g}}C_{g}}} & (17)\end{matrix}$

Accordingly, the flyback voltage V_(fly) in the case where the plasmareactor 3 is broken or suffers wire breakage is greater than the flybackvoltage V_(fly) in the case where the plasma reactor 3 is not broken anddoes not suffer wire breakage.

As shown in FIG. 8, the flyback voltage V_(fly) is generated in thedischarge period T_(dis). A curve L5 represented by a continuous lineshows the flyback voltage V_(fly) for the case where the plasma reactor3 is normal. A curve L6 represented by a continuous line shows theflyback voltage V_(fly) for the case where the plasma reactor 3 isbroken or suffers wire breakage.

Accordingly, in S150, the CPU 51 first outputs from the voltage outputterminal 54 the PWM signal having a duty ratio for initial diagnosis.The CPU 51 then calculates the flyback voltage V_(fly) based on thevoltage input from the voltage detection circuit 40 to the voltage inputterminal 56. Subsequently, the CPU 51 determines whether or not thecalculated flyback voltage V_(fly) is higher than an open determinationvoltage set beforehand. In the case where the flyback voltage V_(fly) ishigher than the open determination voltage, the CPU 51 sets an initialopen flag provided in the RAM 53. Meanwhile, in the case where theflyback voltage V_(fly) is equal to or lower than the open determinationvoltage, the CPU 51 clears the initial open flag.

After completing the process of S150, as shown in FIG. 4, the CPU 51diagnoses a deterioration anomaly of the plasma reactor 3 in S160. Thedeterioration anomaly of the plasma reactor 3 means, for example, thatof the space between the discharge electrode 11 and the dischargeelectrode 12 is clogged with soot.

First, a method of detecting deterioration of the plasma reactor 3 willbe described.

When the space between the discharge electrode 11 and the dischargeelectrode 12 is clogged with soot, the capacitance C_(g) of thecapacitor 16 increases. When the capacitance C_(g) of the capacitor 16in a state in which clogging with soot has occurred in the plasmareactor 3 is denoted by C_(gc), the relation represented by Equation(18) holds.

Further, when the capacitance of the plasma reactor 3 in the state inwhich clogging with soot has occurred in the plasma reactor 3 is denotedby C_(clog), the relation represented by Equation (19) holds.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack & \; \\{C_{gc}C_{d}} & (18) \\{C_{clog} = {\frac{C_{d}C_{gc}}{C_{d} + C_{gc}}C_{c}}} & (19)\end{matrix}$

Accordingly, the flyback voltage V_(fly) in the case where clogging withsoot has occurred is smaller than the flyback voltage V_(fly) in thecase where clogging with soot has not yet occurred.

As shown in FIG. 8, the flyback voltage V_(fly) is generated in thedischarge period Tdis. The curve L5 represented by a continuous lineshows the flyback voltage V_(fly) for the case where the plasma reactor3 is normal. A curve L7 represented by a continuous line shows theflyback voltage V_(fly) for the case where clogging with soot hasoccurred in the plasma reactor 3.

Accordingly, in S160, the CPU 51 first outputs from the voltage outputterminal 54 a PWM signal having a duty ratio for initial diagnosis. TheCPU 51 then calculates the flyback voltage V_(fly) based on the voltageinput from the voltage detection circuit 40 to the voltage inputterminal 56. Subsequently, the CPU 51 determines whether or not thecalculated flyback voltage V_(fly) is lower than a deteriorationdetermination voltage set beforehand. In the case where the flybackvoltage V_(fly) is lower than the deterioration determination voltage,the CPU 51 sets an initial deterioration flag provided in the RAM 53.Meanwhile, in the case where the flyback voltage V_(fly) is equal to orhigher than the deterioration determination voltage, the CPU 51 clearsthe initial deterioration flag.

After completing the S160 process, the CPU 51 ends the initialdiagnosing process as shown in FIG. 4.

After completing the initial diagnosing process, as shown in FIG. 3, inS30, the CPU 51 determines, based on engine drive information receivedperiodically from the engine ECU 2, whether or not the vehicle enginehas started. The engine drive information is information representingthe operating state of the engine (for example, the engine rotationalspeed).

In the case where the engine has not yet started, the CPU 51 waits untilthe engine starts by repeating the process of S30. When the enginestarts, the CPU 51 executes initial control in S40. Specifically, theCPU 51 outputs from the voltage output terminal 54 a PWM signal having amaximum duty ratio set beforehand (in the present embodiment, forexample, 45%), thereby generating plasma in the plasma reactor 3.

The CPU 51 then obtains data of consumed energy, exhaust gastemperature, soot density, and atmospheric pressure in the period duringwhich the plasma reactor 3 is driven at the maximum duty ratio(hereinafter referred to as the “initial drive period”).

The consumed energy is the energy consumed by the discharge in theplasma reactor 3 during the initial drive period. The CPU 51 repeatedlycalculates the supply energy E_(sup) and the regeneration energy E_(reg)during the initial drive period. Also, during the initial drive period,the CPU 51 repeatedly calculates the difference between the supplyenergy E_(sup) and the regeneration energy E_(reg) by subtracting theregeneration energy E_(reg) from the supply energy E_(sup). Also, theCPU 51 integrates the difference calculated during the initial driveperiod, thereby calculating the consumed energy. The CPU 51 uses thecalculated value of the consumed energy as the data of the consumedenergy.

Also, the CPU 51 receives, during the initial drive period, exhaust gastemperature information transmitted periodically from the engine ECU 2and uses, as the data of the exhaust gas temperature, the value of theexhaust gas temperature represented by the received exhaust gastemperature information. The CPU 51 receives, during the initial driveperiod, soot density information transmitted periodically from theengine ECU 2 and uses, as the data of the soot density, the value of thesoot density represented by the received soot density information. TheCPU 51 receives, during the initial drive period, atmospheric pressureinformation transmitted periodically from the engine ECU 2 and uses, asthe data of the atmospheric pressure, the value of the atmosphericpressure represented by the received atmospheric pressure information.

Further, the CPU 51 calculates the amount of soot removed during theinitial drive period (hereinafter referred to as the “initial removedsoot amount”) based on the data of the soot density obtained during theinitial drive period. Subsequently, the CPU 51 determines a correctioncoefficient with reference to a correction coefficient calculation mapin which the correction coefficient is set beforehand while the consumedenergy, the initial removed soot amount, the exhaust gas temperature,and the atmospheric pressure are used as parameters. The correctioncoefficient is used in the process of S54.

Next, in S50, the CPU 51 determines whether or not an execution period(in the present embodiment, for example, 1 sec) set beforehand haselapsed. Specifically, the CPU 51 determines whether or not the value ofan execution timer provided in the RAM 53 is equal to or greater than avalue corresponding to the execution period. The execution timer is atimer which is incremented (namely, one is added to the value of thetimer) at intervals of, for example, 1 ms. When the execution timer isstarted, its value is incremented from 0.

In the case where the execution period has not yet elapsed, the CPU 51waits until the execution period elapses by repeating the process ofS50. When the execution period elapses, the CPU 51 starts the executiontimer in S52.

Next, in S54, the CPU 51 determines a target consumed energy based onthe obtained latest data of the exhaust gas temperature, the sootdensity, and the atmospheric pressure, while referring to a targetcalculation map in which the target consumed energy is set beforehandwhile the exhaust gas temperature, the soot density, and the atmosphericpressure are used as parameters. Furthermore, the CPU 51 calculates acorrected target energy by multiplying the determined target consumedenergy by the correction coefficient determined in S40.

Also, in S56, the CPU 51 calculates the supply energy E_(sup) based onthe inputted latest supply current integration voltage V_(isi) inaccordance with Equation (7). Also, the CPU 51 calculates theregeneration energy E_(reg) based on the inputted latest regenerationcurrent integration voltage V_(iri) in accordance with Equation (8).Further, the CPU 51 calculates a control energy by subtracting thecalculated regeneration energy E_(reg) from the calculated supply energyE_(sup).

Subsequently, in S58, the CPU 51 calculates the duty ratio of the PWMsignal such that the deviation between the calculated corrected targetenergy and the calculated control energy becomes zero through, forexample, feedback control using a proportional gain, an integral gain,and a derivative gain (i.e., PID control). The CPU 51 then outputs fromthe voltage output terminal 54 a PWM signal having the calculated dutyratio.

Next, the CPU 51 executes a purification-time diagnosing process in S60.

Here, the steps of the purification-time diagnosing process will bedescribed.

In the purification-time diagnosing process, as shown in FIG. 5, the CPU51 first performs a process of protecting the driver 32 from overheatingin S210. Specifically, the CPU 51 first determines whether or not thetemperature represented by the detection signal from the temperaturesensor 8 (hereinafter referred to as the “driver temperature”) is equalto or higher than a failure determination temperature set beforehand. Inthe case where the driver temperature is equal to or higher than thefailure determination temperature, the CPU S1 sets a driver overheatflag provided in the RAM 53, and prohibits the output of the PWM signalfrom the voltage output terminal 54. Meanwhile, in the case where thedriver temperature is lower than the failure determination temperature,the CPU 51 clears the driver overheat flag.

Next, in S220, the CPU 51 diagnoses an anomaly of the voltage of thebattery 5. Specifically, the CPU 51 determines whether or not the powersupply voltage falls within the operating voltage range in a mannersimilar to that in S120. In the case where the power supply voltagefalls within the operating voltage range, the CPU 51 clears apurification-time voltage anomaly flag provided in the RAM 53.Meanwhile, in the case where the power supply voltage falls outside theoperating voltage range, the CPU 51 sets the purification-time voltageanomaly flag.

Next, in S230, the CPU 51 executes a process of protecting the driver 32from overvoltage. Specifically, the CPU 51 first calculates the flybackvoltage V_(fly) based on the voltage input from the voltage detectioncircuit 40 to the voltage input terminal 56. Subsequently, the CPU 51determines whether or not the calculated flyback voltage V_(fly) isequal to or higher than a failure determination voltage set beforehand.In the case where the flyback voltage V_(fly) is equal to or higher thanthe failure determination voltage, the CPU 51 sets a driver overvoltageflag provided in the RAM 53, and prohibits the output of the PWM signalfrom the voltage output terminal 54. Meanwhile, in the case where theflyback voltage V_(fly) is lower than the failure determination voltage,the CPU 51 clears the driver overvoltage flag.

Next, in S240, the CPU 51 diagnoses an internal failure of thetransformer 4. Specifically, as in S130, when the driver 32 is in the onstate, the CPU 51 determines, based on the voltage V_(ip) input from thecurrent detection circuit 37 to the voltage input terminal 57, whetheror not the primary coil current value is smaller than the transformerwire-breakage determination value. In the case where the primary coilcurrent value is smaller than the transformer wire-breakagedetermination value, the CPU 51 sets a purification-time wire-breakageanomaly flag provided in the RAM 53. Meanwhile, in the case where theprimary coil current value is equal to or larger than the transformerwire-breakage determination value, the CPU 51 clears thepurification-time wire-breakage anomaly flag.

Next, in S250, the CPU 51 diagnoses an open anomaly of the plasmareactor 3. Specifically, the CPU 51 first calculates the flyback voltageV_(fly) based on the voltage input from the voltage detection circuit 40to the voltage input terminal 56 in a manner similar to that in S150.The CPU 51 then determines whether or not the calculated flyback voltageV_(fly) is higher than the open determination voltage. In the case wherethe flyback voltage V_(fly) is higher than the open determinationvoltage, the CPU 51 sets a purification-time open flag provided in theRAM 53. Meanwhile, in the case where the flyback voltage V_(fly) isequal to or lower than the open determination voltage, the CPU 51 clearsthe purification-time open flag.

After completing the S250 process, the CPU 51 ends the purification-timediagnosing process.

After ending the purification-time diagnosing process, as shown in FIG.3, in S70, the CPU 51 determines, based on the engine drive informationreceived periodically from the engine ECU 2, whether or not the engineof the vehicle has stopped. In the case where the engine has not yetstopped, the CPU 51 proceeds to S50. Meanwhile, in the case where theengine stops, the CPU 51 ends the discharge control process.

Next, a specific example of operation of the discharge control apparatus6 will be described.

As shown in FIG. 10, when the PWM signal changes from the low level tothe high level at time t₁, the gate control voltage V_(gs) changes fromthe low level to the high level. As a result, the primary current I_(p)increases gradually, and the primary inter-terminal voltage V_(p)becomes equal to the power supply voltage VB. Also, as a result of theincrease in the primary current I_(p), the supply current integrationvoltage V_(isi) increases gradually.

When the PWM signal changes from the high level to the low level at timet₂, the gate control voltage V_(gs) changes from the high level to thelow level. As a result, the primary current I_(p) decreases sharply andbecomes 0 [A]. Also, the primary inter-terminal voltage V_(p) decreasessharply to the negative side, and the secondary inter-terminal voltageV_(s) increases sharply, so that discharge is generated in the plasmareactor 3. Also, the flyback voltage V_(fly) increases sharply.

The discharge generation continues from time t₂ to time t₃. After thedischarge ends, the primary current I_(p) attenuates while oscillatingon the negative side, and becomes 0 [A] at time t₄. The primary currentI_(p) flowing from time t₃ to time t₄ is the regeneration current. Theprimary inter-terminal voltage V_(p) becomes equal to the power supplyvoltage VB in the period between time t₃ and time t₄, and becomes 0 [V]at time t₄. The secondary inter-terminal voltage V_(s) attenuates whileoscillating between the positive and negative sides in the periodbetween time t₃ and time t₄.

Also, due to the primary current I_(p) flowing from time t₃ to time t₄,the regeneration current integration voltage V_(iri) increasesgradually. Also, the output voltage V_(isr) of the regenerationdetection circuit 38 changes from the low level to the high level attime t and changes from the high level to the low level at time t₄. Whenthe output voltage V_(isr) changes from the low level to the high level,the supply current integration voltage V_(isi) is reset to 0 [V].Notably, in accordance with the output voltage V_(isr) of theregeneration detection circuit 38, the gate control voltage V_(gs)changes from the low level to the high level at time it and changes fromhigh level to the low level at time t₄.

When the voltage V_(irr) of the voltage output terminal 54 changes fromthe low level to the high level at time t₅ at which the gate controlvoltage V_(gs) changes from the low level to the high level, theregeneration current integration voltage V_(iri) is reset to 0 [V].

The discharge control apparatus 6 configured as described above controlsthe flyback power supply circuit. The power supply circuit comprises thetransformer 4 having the primary coil 21 and the secondary coil 22 andwhich performs voltage conversion, and the driver 32 for controllingenergization of the primary coil 21. The power supply circuit supplieselectric energy to the plasma reactor 3 which generates plasma bydischarge.

The discharge control apparatus 6 calculates, based on the primarycurrent I_(p) flowing through the primary coil 21 and the inter-terminalvoltage V_(p) generated in the primary coil 21, the supply energyE_(sup) supplied to the primary coil 21 and the regeneration energyE_(reg) which is a portion of the supply energy E_(sup) not used for thedischarge in the plasma reactor 3.

The discharge control apparatus 6 controls the power supply circuitbased on the calculated supply energy E_(sup) and the calculatedregeneration energy E_(reg).

As described above, the discharge control apparatus 6 calculates thesupply energy E_(sup) and the regeneration energy E_(reg) based on theprimary current I_(p) flowing through the primary coil 21 and theinter-terminal voltage V_(p) generated in the primary coil 21, andcontrols the power supply circuit based on the supply energy E_(sup) andthe regeneration energy E_(reg). By virtue of this configuration, thedischarge control apparatus 6 can control the power supply circuitwithout use of the secondary current flowing through the secondary coil22 and the secondary voltage generated in the secondary coil 22.Therefore, the discharge control apparatus 6 can eliminate the necessityof a component or assembly for securing insulation, thereby reducingproduction cost or simplifying apparatus configuration.

In the above-described embodiment, the transformer 4 and the driver 32correspond to the power supply circuit; and the inter-terminal voltageV_(p) corresponds to the primary voltage.

Also, S56 corresponds to the process performed by the energy calculationsection and the process performed as the energy calculation step, andS58 corresponds to the process performed by the control section and theprocess performed as the control step.

One embodiment of the present disclosure has been described; however,the present disclosure is not limited to the above-described embodimentand various modifications are possible.

For example, in the above-described embodiment, the supply energyE_(sup) and the regeneration energy E_(reg) are calculated usingEquations (7) and (8). However, the supply energy E_(sup) and theregeneration energy E_(reg) may be calculated using Equations (9) and(10).

Also, the function of one constituent element in the above-describedembodiment may be distributed to a plurality of constituent elements, orthe functions of a plurality of constituent elements may be realized byone constituent element. Part of the configuration of theabove-described embodiment may be omitted. Also, at least part of theconfiguration of the above-described embodiment may be added to orpartially replace the configurations of other embodiments.

The present disclosure may be realized in various forms other than theabove-described discharge control apparatus 6. For example, the presentdisclosure may be realized as a system including the discharge controlapparatus 6 as a constituent element, a program for causing a computerto function as the discharge control apparatus 6, a non-transitorytangible recording medium, such as semiconductor memory, on which theprogram is recorded, and a discharge control method.

The invention has been described in detail with reference to the aboveembodiments. However, the invention should not be construed as beinglimited thereto. It should further be apparent to those skilled in theart that various changes in form and detail of the invention as shownand described above may be made. It is intended that such changes beincluded within the spirit and scope of the claims appended hereto.

This application is based on Japanese Patent Application No. JP2019-067882 filed Mar. 29, 2019, the disclosure of which is incorporatedherein by reference in its entirety.

What is claimed is:
 1. A discharge control apparatus for controlling aflyback power supply circuit which includes a transformer having aprimary coil and a secondary coil and which performs voltage conversion,and a driver for controlling energization of the primary coil and whichsupplies electric energy to a plasma reactor which generates plasma bydischarge, the discharge control apparatus comprising: an energycalculation section configured to calculate, based on primary currentflowing through the primary coil and primary voltage generated in theprimary coil, supply energy supplied to the primary coil andregeneration energy which is a portion of the supply energy not used forthe discharge in the plasma reactor; and a control section configured tocontrol the power supply circuit based on the supply energy andregeneration energy calculated by the energy calculation section.
 2. Thedischarge control apparatus as claimed in claim 1, wherein the energycalculation section calculates the supply energy in accordance with thefollowing Equation (1) and calculates the regeneration energy inaccordance with the following Equation (2):E _(sup)=∫_(t) ₁ ^(t) ² V _(p) ·I _(p) dt  (1)E _(reg)=∫_(t) ₃ ^(t) ⁵ V _(p) ·I _(p) dt  (2) where E_(sup) representsthe supply energy, E_(reg) represents the regeneration energy, I_(p)represents the value of the primary current, V_(p) represents the valueof the primary voltage, and wherein the time period during which thesupply energy is generated is denoted a period from time t₁ to time t₂and the time period during which the regeneration energy is generated isdenoted a period from time t₃ to time t₅.
 3. A discharge control methodfor controlling a flyback power supply circuit which includes atransformer having a primary coil and a secondary coil and performingvoltage conversion, and a driver for controlling energization of theprimary coil and which supplies electric energy to a plasma reactorwhich generates plasma by discharge, the discharge control methodcomprising: an energy calculation step of calculating, based on primarycurrent flowing through the primary coil and primary voltage generatedin the primary coil, supply energy supplied to the primary coil andregeneration energy which is a portion of the supply energy not used forthe discharge in the plasma reactor, and a control step of controllingthe power supply circuit based on the supply energy and the regenerationenergy calculated by the energy calculation step.